linux-kernel - Re: [PATCH] framewarn: expand KASAN

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Date:   Fri, 21 Sep 2018 14:11:54 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] framewarn: expand KASAN_EXTRA exception to KASAN

On Fri, Sep 21, 2018 at 10:42 AM, 'Dmitry Vyukov' via kasan-dev
<kasan-dev@...glegroups.com> wrote:
> On Fri, Sep 21, 2018 at 3:50 AM, Andy Lutomirski <luto@...nel.org> wrote:
>> This patch seems reasonable, but you emailed the wrong people :)
>>
>> On Thu, Sep 20, 2018 at 5:15 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>>>
>>> It turns out that KASAN in general will bloat stack frames in unexpected
>>> ways, not just KASAN_EXTRA. So, this patch trivially changes that
>>> default to be associated with KASAN instead of KASAN_EXTRA.
>>>
>>> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
>>> ---
>>>  lib/Kconfig.debug | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>>> index 4966c4fbe7f7..39078a080e29 100644
>>> --- a/lib/Kconfig.debug
>>> +++ b/lib/Kconfig.debug
>>> @@ -222,7 +222,7 @@ config ENABLE_MUST_CHECK
>>>  config FRAME_WARN
>>>         int "Warn for stack frames larger than (needs gcc 4.4)"
>>>         range 0 8192
>>> -       default 3072 if KASAN_EXTRA
>>> +       default 3072 if KASAN
>>>         default 2048 if GCC_PLUGIN_LATENT_ENTROPY
>>>         default 1280 if (!64BIT && PARISC)
>>>         default 1024 if (!64BIT && !PARISC)
>
>
> Looks fine to me.
> KASAN always increases stack size too for exactly that reason, so it's
> reasonable to allow larger frames rather than try to massage code
> every here and there to fit into the normal frame size.

Do we need KASAN_EXTRA then at all?